WASHINGTON – The Obama administration on Sunday turned up the heat on Russia for its support of Ukrainian separatists accused by the United States and others of shooting down a Malaysian passenger plane.

In some of the administration's harshest criticism of Russia since the crisis in Ukraine began earlier this year, Secretary of State John Kerry outlined the U.S. case that the separatists are to blame for the downing of the aircraft and that Russia was almost certainly complicit. He demanded that Russia act immediately to rein in the rebels and to actively support a transparent investigation into what happened to the plane.

"This is the moment of truth for Russia," Kerry said. "Russia is supporting these separatists. Russia is arming these separatists. Russia is training these separatists, and Russia has not yet done the things necessary in order to try to bring them under control."

In addition, he said the administration was hopeful that the shoot-down would galvanize support in Europe for increasing sanctions on Russia over its overall actions in Ukraine.

"We hope this is a wake-up call for some countries in Europe that have been reluctant to move," Kerry said, recalling that President Barack Obama had signed off on a new round of sanctions on Russia the day before the plane went down Thursday.

In a round of television interviews, Kerry cited a mix of U.S. intelligence and social media reports that he said "obviously points a very clear finger at the separatists" for firing a Russian-provided SA-11 surface-to-air missile that brought the plane down, killing nearly 300 passengers and crew.

"It's pretty clear that this is a system that was transferred from Russia into the hands of separatists," he said.

Video of an SA-11 launcher, with one of its missiles missing and leaving the likely launch site, has been authenticated, he said.

An Associated Press journalist saw a missile launcher in rebel-held territory close to the crash site just hours before the plane was brought down.

Kerry added that separatists had shot down about 12 aircraft over the past month, and had bragged in the phone intercepts about Thursday's attack until they realized it was a commercial jet.

Kerry said Russian President Vladimir Putin must live up to his commitment to press for a full and independent international investigation into the jet's downing and use his influence with the separatists who have taken the plane's black box flight recorders, removed the victims' bodies and "seriously compromised" the crash site. "This is an insult to everybody," he said.

"This is a fundamental moment of truth for Russia, for Mr. Putin," Kerry said. "They need to exert all of the influences they have in order to protect the full integrity of this investigation."

The U.S. and Ukrainian authorities have been at the forefront of accusations that the separatists, aided by Russia, are responsible although other countries, including Australia and Britain have offered similar, if less definitive, assessments. On Sunday, British Prime Minister David Cameron said in an unusual front-page piece in the Sunday Times that there is growing evidence that separatist rebels, backed by Russia, shot down the aircraft.

"If President Putin does not change his approach to Ukraine, then Europe and the West must fundamentally change our approach to Russia," Cameron wrote.

Cameron, French President Francois Hollande and German Chancellor Angela Merkel demanded that Putin force separatists controlling the site to "finally allow rescuers and investigators to have free and total access to the zone." If Russia fails "to immediately take the needed measures, consequence will be drawn" at an EU foreign ministers meeting set for Tuesday, a statement from Hollande's office said.

In his interviews, Kerry accused Russia of "playing" a dual-track policy in Ukraine of saying one thing and doing another. That, he said, "is really threatening both the larger interests as well as that region and threatening Ukraine itself."

He lamented that the level of trust between Washington and Moscow is now at a low ebb, saying it "would be ridiculous at this point in time to be trusting" of what the Kremlin says.

Putin and other Russian officials have blamed the government in Ukraine for creating the situation and atmosphere in which the plane was downed, but have yet to directly address the allegations that the separatists were responsible or were operating with technical assistance from Moscow.

Kerry made his comments in appearance on five talk shows: CNN's "State of the Union," ''Fox News Sunday," CBS's "Face the Nation," NBC's "Meet the Press," and ABC's "This Week."